Study of metalation of thioredoxin by gold(I) therapeutic compounds using combined liquid chromatography/capillary electrophoresis with inductively coupled plasma/electrospray MS/MS detection

The reactivity of thioredoxin (Trx1) with the Au(I) drug auranofin (AF) and two therapeutic N-heterocyclic carbene (NHC)2-Au(I) complexes (bis [1-methyl-3-acridineimidazolin-2-ylidene]gold(I) tetrafluoroborate (Au3BC) and [1,3-diethyl-4,5-bis(4methoxyphenyl)imidazol-2-ylidene]gold(I) (Au4BC)) was investigated. Direct infusion (DI) electrospray ionization (ESI) mass spectrometry (MS) allowed information on the structure, stoichiometry, and kinetics of formation of Trx-Au adducts. The fragmentation of the formed adducts in the gas phase gave insights into the exact Au binding site within the protein, demonstrating the preference for Trx1 Cys32 or Cys35 of AF or the (NHC)2-Au(I) complex Au3BC, respectively. Reversed-phase HPLC suffered from the difficulty of elution of gold compounds, did not preserve the formed metal-protein adducts, and favored the loss of ligands (phosphine or NHC) from Au(I). These limitations were eliminated by capillary electrophoresis (CE) which enabled the separation of the gold compounds, Trx1, and the formed adducts. The ICP-MS/MS detection allowed the simultaneous quantitative monitoring of the gold and sulfur isotopes and the determination of the metallation extent of the protein. The hyphenation of the mentioned techniques was used for the analysis of Trx1-Au adducts for the first time.

A physicochemical investigation on the metal binding properties of TtSmtB, a thermophilic member of the ArsR/SmtB transcription factor family

The transcription factors of the ArsR/SmtB family are widespread within the bacterial and archaeal kingdoms. They are transcriptional repressors able to sense a variety of metals and undergo allosteric conformational changes upon metal binding, resulting in derepression of genes involved in detoxification. So far, the molecular determinants of specificity, selectivity, and metal binding mechanism have been scarcely investigated in thermophilic microorganisms. TtSmtB, the only ArsR/SmtB member present in the genome of Thermus thermophilus HB27, was chosen as a model to shed light into such molecular mechanisms at high temperature. In the present study, using a multidisciplinary approach, a structural and functional characterization of the protein was performed focusing on its metal interaction and chemical-physical stability. Our data demonstrate that TtSmtB has two distinct metal binding sites per monomer and interacts with di-tri-penta-valent ions with different affinity. Detailed knowledge at molecular level of protein-metal interaction is remarkable to design metal binding domains as scaffolds in metal-based therapies as well as in metal biorecovery or biosensing in the environment.

De Novo Design of Metalloproteins and Metalloenzymes in a Three-Helix Bundle

For more than two decades, de novo protein design has proven to be an effective methodology for modeling native proteins. De novo design involves the construction of metal-binding sites within simple and/or unrelated α-helical peptide structures. The preparation of α3D, a single polypeptide that folds into a native-like three-helix bundle structure, has significantly expanded available de novo designed scaffolds. Devoid of a metal-binding site (MBS), we incorporated a 3Cys and 3His motif in α3D to construct a heavy metal and a transition metal center, respectively. These efforts produced excellent functional models for native metalloproteins/metalloregulatory proteins and metalloenzymes. Morever, these α3D derivatives serve as a foundation for constructing redox active sites with either the same (e.g., 4Cys) or mixed (e.g., 2HisCys) ligands, a feat that could be achieved in this preassembled framework. Here, we describe the process of constructing MBSs in α3D and our expression techniques.